Conventional boiling water reactors include a reactor pressure vessel (RPV) which surrounds a core shroud. The core shroud, in turn, surrounds a reactor core. Generally, each of the core shroud and the reactor pressure vessel are cylindrically shaped such that an outer diameter of the core shroud is less than an inner diameter of the reactor pressure vessel. Between a reactor pressure vessel wall and a core shroud wall is an annular space in which jet pump assemblies are typically located.
FIG. 1 illustrates a conventional jet pump assembly 25 located in the aforementioned annulus. As illustrated in FIG. 1, an inlet nozzle 10 extending through a sidewall 15 of RPV 20 is coupled to jet jump assembly 25. Jet pump assembly 25 includes a riser pipe 30 that extends between shroud 35 and sidewall 15 of RPV 20. Riser pipe 30 is coupled to two jet pumps 35A and 35B by a transition assembly 40. Each jet pump 35A and 35B includes a jet pump nozzle 42, a suction inlet 45, an inlet mixer 50, and a diffuser 55. For example, first jet pump 35A includes a first inlet mixer 50A and second jet pump 35B includes second inlet mixer 50B. Jet pump nozzles 42 are positioned in the suction inlets 45 that are located at a first end of inlet mixers 50A and 50B. Diffusers 55 are coupled to a second end of inlet mixers 50A and 50B by a slip joint 65. Typically, both inlet mixers 50A and 50B and diffusers 55 are formed of multiple cylindrical sections. Circumferential welds 70 join the cylindrical sections together. A support member (riser brace) 75 typically surrounds riser pipe 30 and connects to riser pipe 30 via a weld 80 which may span approximately 180 degrees around the circumference of the riser pipe 30. Inlet mixers 50A and 50B are secured to riser pipe 30 via a restrainer bracket 105.
As shown in FIG. 2, conventional restrainer bracket 105 is a yoke-like member surrounding the inlet mixer 50A at a belly band 195 of inlet mixer 50A. Though not shown, a similar yoke-like restrainer bracket surrounds mixer 50B. Penetrating the restrainer bracket 105 are at least two set screws 110 which press against the inlet mixer belly band 195. In FIG. 2, only one set screw 110 is shown. Inlet mixer 50A further includes several guide ears 190 arranged about, and extending from, outer edges of restrainer bracket 105. A strengthening rib 191 may also be present between an edge and lip of restrainer bracket 105 to provide rigid support to the restrainer bracket 105. A main wedge 115 is typically provided between a restrainer bracket pad 145 of restrainer bracket 105 and inlet mixer belly band 195. The main wedge 115 includes a circular hole through which a wedge rod 130 passes. The wedge rod 130 has a threaded top end 131 which connects to an upper support casting 120 arranged above restrainer bracket 105 and a threaded bottom end which connects to a lower support casting 125 below restrainer bracket 105. As inlet mixer 50A moves vertically or horizontally, wedge 115 may slide on wedge rod 130 and, through contact between restrainer bracket pad 145, wedge 115, and restrainer bracket belly band 195, such motion of the inlet mixer 50A may be nondestructively opposed and reduced.